how to implement that in core data

in SQL we use the following clause

where studentName like '%a' and StudentID = 1

how to do that in objective c and core data using setpredic开发者_如何学Pythonate for fetchrequest

I have only two inputs part of the name @"a" and the ID @"1"

best regards

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Take a look at the Predicate Programming Guide.

I would also like to add the Core Data Programming Guide - Fetching Managed Objects.

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it worked with contains[cd] but I want to know what if I passed the string empty and want to search by ID only

Normally, you don't use empty strings in a fetch predicate because core data will try to match the empty string. Instead, you should create different fetch request for different circumstances. Fetch request are lightweight objects than can be stored in arrays (or even the data model itself.)

If this case, you would test for an empty string and if true use a fetch predicate that only looks for the StudentID.

In general, try to avoid thinking of Core Data in SQl terms. It's natural but dangerous. Core Data is not SQL. Entities are not tables. Objects are not rows. Columns are not attributes. Core Data is an object graph management system that may or may not persist the object graph and may or may not use SQL far behind the scenes to do so. Trying to think of Core Data in SQL terms will cause you to completely misunderstand Core Data and result in much grief and wasted time.

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I agree with TechZen, you should be thinking of core data in terms of objects, as opposed to being sql backed. CD uses SQL as an implementation detail, not necessarily as a defining feature.

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This is an example from the developer library

Creating Fetch Request Templates Programmatically

basicly it looks something like this using predicated...

NSManagedObjectModel *model = <#Get a model#>;
NSFetchRequest *requestTemplate = [[NSFetchRequest alloc] init];
NSEntityDescription *publicationEntity =
    [[model entitiesByName] objectForKey:@"Publication"];
[requestTemplate setEntity:publicationEntity];

NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:
    @"(mainAuthor.firstName like[cd] $FIRST_NAME) AND \
        (mainAuthor.lastName like[cd] $LAST_NAME) AND \
        (publicationDate > $DATE)"];
[requestTemplate setPredicate:predicateTemplate];

[model setFetchRequestTemplate:requestTemplate
    forName:@"PublicationsForAuthorSinceDate"];
[requestTemplate release];

so by looking at that your probably after something like this

NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:
        @"(mainAuthor.firstName like[cd] $FIRST_NAME) AND \
            (mainAuthor.lastName like[cd] $LAST_NAME) AND \
            (publicationDate > $DATE)"];
    [requestTemplate setPredicate:predicateTemplate];

hope this helps I'm currently setting up core data in my project and have been reading through this stuff all morning.